A photo-responsive nanogel was synthesized from spiropyran (SP) methacrylate. Spiropyran undergoes a photochromic switching from a neutral to a zwitterionic structure under UV irradiation. Isomerization of the pendant SP functionality within the nanogel leads to a change in hydrophilicity that can induce swelling or deswelling depending on the polarity of the monomer used to disperse and infiltrate the 6 nm nanogel particles. With 0.1 to 2 wt% of the SP-modified nanogel added to triethylene glycol dimethacrylate (TEGDMA), colorless, transparent homogenous mixtures were obtained. Upon UV irradiation in the presence of photoinitiator, formation of the glassy, crosslinked polymer is coupled with the rapid photo-switching in the dispersed nanogel structures with potential significant dimensional change. The practical utility is that this provides a new mechanism to alleviate polymerization-induced stress. The formulation with 1 wt% SP nanogel reduced stress by 50 % compared to the TEGDMA control. Although the photochromism process competes for the same photons necessary to initiate polymerization, photopolymerization kinetics were only modestly affected for this range of nanogel-modified systems. Interesting surface morphology differences were noted with a change from a wrinkled pattern to a needle-like pattern as the nanogel content was increased.

Photoresponsive nanogels for polymer network modification

246th National Meeting (2013)

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